#include <stdio.h>
#include <errno.h>
#include <string.h>

extern int errno;

int main(){
    FILE *fp;
    int errnum;
    fp=fopen("unexist.txt","rb");
    if(fp==NULL){
        errnum=errno;
        fprintf(stderr,"Error Number: %d\n",errno);
        perror("Print Error by perror");
        fprintf(stderr,"File open error: %s\n",strerror(errnum));
    }else{
        fclose(fp);
    }
    return 0;
}
